Lanthanide Oxide Nanoparticles and their Nanocomposites

Novel lanthanide oxide and hydroxide based nanostructures which show optical luminescence were prepared and incorporated into polymers. The surface-functionalization of these objects and the polymer matrix plays a major role for the emission of these materials. Lanthanide-based materials are widely known for their optical properties, which makes them useful compounds for novel light emitting devices. In this project binary oxide and hydroxide nanostructures were prepared and incorporated into organic polymers. The scientific focus was lying on the control of optical properties of the obtained materials. One of the major problems in the synthesis of lanthanide oxide nanoobjects is the possible switch in oxidation states and thus the generation of non-uniform materials. We solved this problem in the project by first preparing the nanoobjects as lanthanide hydroxides and transforming these compounds under mild conditions into the oxides. This method allowed us to keep the surface-functionalization unaffected during the transformation. A variety of nanoobjects was prepared, in particular anisotropic nanorods, with different types of organic molecules attached to their surface. Some of these systems showed an antenna effect, which means that the organic surface-function harvested light and transferred the energy to the metal ions of the nanorod which were emitting light of another wavelength. The thus obtained nanoobjects were incorporated into a polymer matrix and luminescent nanocomposites were obtained. Nanocomposites incorporating lanthanide-based nanostructures were also obtained applying a different approach in which a crosslinked polymer matrix was prepared in a first step and the inorganic nanoobjects were formed inside of the swollen polymer matrix in a second step. Optical transparent hydrophobic polysiloxanes crosslinked by hydrophilic poly(ethylene oxides) (PEO) were used as the polymer matrix in this approach. The applied matrix revealed a high optical transparency and chemical stability and could be tuned in terms of swellability and hydrophilicity by systematic variation of the PEO chain length and the ratios between the PEO and polysiloxane segments. Infiltration of the polymer matrix with solutions of various lanthanide salts and subsequent hydrolysis created nanoparticles inside of the polymer matrix. The europium-doped nanocomposites exhibited room temperature emission and an energy transfer from the host polymer matrix to the europium ions. The host matrix was also able to direct the structure development, resulting in either nanorods or -particles dependent on the polymer composition. Furthermore, other metal nanoparticles, such as cobalt or gold, were also incorporated into this matrix material which resulted in flexible polymers with ferromagnetic, in case of cobalt, or specific optical properties as a consequence of gold nanoparticle incorporation.